The present invention relates to atomic force microscopy and specifically to an atomic force microscope which employs a micromachined cantilever beam in order to achieve atomic resolution. In addition, the atomic force microscope is capable of operation in vacuum, air or liquid environments, of scanning a large surface area and of providing common mode rejection for improved operation.
Atomic force microscopy is based upon the principle of sensing the forces between a sharp stylus or tip and the surface to be investigated. The interatomic forces induce the displacement of the stylus mounted on the end of a cantilever beam. In its original implementation, a tunneling junction was used to detect the motion of the stylus attached to an electrically conductive cantilever beam. Subsequently, optical interferometry was used to detect cantilever beam deflection.
As described by G. Binnig et al, in Phys. Rev. Lett., vol. 56, No. 9, March 1986, pp. 930-933, a sharply pointed tip is attached to a spring-like cantilever beam to scan the profile of a surface to be investigated. The attractive or repulsive forces occurring between the atoms at the apex of the tip and those of the surface result in tiny deflections of the cantilever beam. The deflection is measured by means of a tunneling microscope. That is, an electrically conductive tunnel tip is disposed within the tunnel distance from the back of the cantilever beam, and the variations of the tunneling current are indicative of the beam deflection. The forces occurring between the tip and the surface under investigation are determined from the measured beam deflection and the characteristics of the cantilever beam.
In articles by G. McClelland et al, entitled "Atomic Force Microscopy: General Principles and a New Implementation", Rev. Progr. Quart. Non-destr. Eval., vol. 6, 1987, p. 1307 and Y. Martin et al, entitled "Atomic force microscope-force mapping and profiling on a sub 100- .ANG. scale", J. Appl. Phys., vol. 61, no. 10, May 15, 1987, pp 4723-4729, there is described the use of a laser interferometer to measure tip displacement. The advantages of optical detection over tunneling detection of the cantilever beam deflection are increased reliability and ease of implementation, insensitivity to the roughness of the beam, and a smaller sensitivity to thermal drift.
The atomic force microscope has a promising future in research and development and in manufacturing environments because of its unique capabilities of imaging insulators and measuring minute forces. In order to fulfill the promise, the atomic force microscope should be versatile, i.e., operate in vacuum, air or aqueous environments and be reliable, simple, and compact. Moreover, for certain applications atomic resolution and the ability to scan larger areas are additional requirements.